This invention relates to an apparatus for measuring the radioactive concentration of a radioactive fluid flowing in pipes, and more particularly to an apparatus for measuring the radioactive concentration of a low-level radioactive waste liquid discharged from a nuclear power plant.
In a nuclear power plant or the facilities in which a radioactive material is handled, it is necessary to measure the radioactive concentration of a liquid flowing in various kinds of pipes provided therein. In, for example, a nuclear power plant, the abnormal condition thereof is detected with reference to a measured radioactive concentration to prevent a fluid of a high radioactive concentration from being discharged to the outside thereof.
There is a known apparatus for measuring the radioactive concentration of a radioactive fluid in the pipes in a nuclear power plant, which is disclosed in Japanese Patent Laid-open No. 137595/1977.
In this apparatus, a measuring pipe through which a waste liquid which contains a radioactive material to be measured, flows is vertically disposed. The waste liquid is passed through the measuring pipe along the axis thereof by the force of gravity in such a manner that the waste liquid does not contact the inner surface thereof. The cleaning water is also introduced into the measuring pipe along the inner surface thereof to prevent the radioactive material from being accumulated thereon. A radiation detector is provided outside the measuring pipe and adapted to measure the radioactive concentration of the waste liquid as the detector is not in contact with the measuring pipe.
In order to measure the low-level radioactivity with this type of apparatus, it is necessary to improve the sensitivity thereof. There is a known apparatus made with a view to meeting this requirement, which is disclosed in Japanese Patent Laid-open No. 46177/1982. In this apparatus, a plurality of detectors are provided around a measuring pipe to measure the radioactive concentration of a fluid flowing therethrough. There the dimensions of the apparatus increase greatly.